<html xmlns="http://www.w3.org/1999/xhtml"  
      xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
      xmlns:math="http://www.w3.org/1998/Math/MathML">
<head></head>
<body>

<xul:box collapsed="true"><math:mrow><div id="div">
<p id="para">Foo bar</p>
</div></math:mrow></xul:box>

<script type="application/javascript">
document.body.offsetWidth;

try
{
  var XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";

  var para = document.getElementById("para");
  var div = document.getElementById("div");
  var hbox = document.createElementNS(XUL_NS, 'hbox');

  div.appendChild(hbox);
  div.removeChild(para);
}
catch (e)
{
  document.body.appendChild(document.createTextNode(e));
}
</script>

</body>
</html>
